In situ retorting of oil shale

ABSTRACT

Initiation and support of the in situ retorting of oil shale is accomplished by injecting the retorting fluid at a multiplicity of points along a substantially horizontal plane in the chimney created by a nuclear explosion. The retorting fluid is injected through an injection well extending generally horizontally in the chimney, preferably in the uppermost portion thereof. A series of such injection wells may be employed in order to provide for the distribution of the retorting fluid substantially across the cross-sectional area of the chimney.

United States Patent Guide 0. Grady Tulsa, Okla.

Apr. 2, 1968 Aug. 24, 1971 Cities Service Oil Co. Tulsa, Okla.

[72] Inventor [21 1 Appl. No. [22] Filed [45] Patented [73] Assignee[54} IN SITU RETORTING OF OIL SHALE 12 Claims, 2 Drawing Figs.

[52] 11.8. C1 166/245, 166/247, 166/259, 166/269, 166/270, 166/272 [51]Int. Cl. E2lb 43/24, E2 lb 43/26 [50] Fieldofsearch 166/1l,36, 39, 40,42, 269, 256-262, 268, 270, 271, 272, 302, V 303, 305, 308, 247, 245

[56] References Cited UNITED STATES PATENTS 1,269,747 6/1918 Rogers166/39 UX 2,974,937 3/1961 Kiel 166/11 X 2,975,834 3/1961 West et al.166/38 X 3,017,168 1/1962 Carr 166/11 X 3,024,013 3/1962 Rogers et a1.166/11 3,223,158 12/1965 Baker 166/11 3,228,468 1/1966 Nichols 166/113,233,668 2/1966 Hamilton et a1. 166/11 X 3,270,813 9/1966 Gilchrist166/38 X 3,342,257 9/1967 Jacobs et a1. 166/36 Primary Examiner-StephenJ. Novosad Attorney-l. Richard Geaman ABSTRACT: Initiation and supportof the in situ retorting of oil shale is accomplished by injecting theretorting fluid at a multiplicity of points along a substantiallyhorizontal plane in the chimney created by a nuclear explosion. Theretorting fluid is injected through an injection well extendinggenerally horizontally in the chimney, preferably in the uppermostportion thereof. A series of such injection wells may be employed inorder to provide for the distribution of the retorting fluidsubstantially across the cross-sectional area of the chimney.

PATENTED Aus24|97| 3601.193

INVENTOR GUIDO o. GRADY FIG-1 Z ATTORNEY IN SITU RETORTING OF OIL SHADEBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to the recovery of hydrocarbons from oil shale. Moreparticularly, it relates to the recovery of shale In situ recoverytechniques are likewise confronted with significant problems. Suchtechniques have not been successful in recovering economical amounts ofshale-oil from the massive oil shale deposits that often are covered byan appreciable overburden. The very low natural permeability of oilshale has been a significant factor in the relative ineffectiveness 'ofin situ retorting techniques. The oil shale must be extensivelyfractured or broken up into a rubble of relatively high and uniformpermeability in order to permit a relatively uniform heat permeationthroughout a substantially impervious natural retorting chamber so as torelease substantially all of the available shale oil from the area beingtreated.

The use of a nuclear explosive device placed near the bottom of the oilshale formation has been proposed. Upon detonation of such a device, alarge, substantially spherical hollow cavity would be createdinstantaneously. This cavity would be surrounded by a thick zone offractured but nevertheless impervious shale or rock. The fractured rocklocated above the cavity would collapse so as to at least partially fillthe cavity. Thus, a substantially cylindrical retortlike zone or chimneyfilled with crumbled and pervious oil shale would result. Such atechnique is described, for example, in the Jacobs et al. patent, U.S.Pat. No. 3,342,257 issued Sept. 19, 1967.

The retorting of the shale in the chimney thus fonned may be initiatedand supported by drilling gas inlet and oil recovery wells to connectthe chimney with on-surface gas-pumping and shale oil recoveryequipment. A hot or heated gas can thereafter be passed throughthe'chimney of crumbled pervious shale, preferably in a downwarddirection, so as to decom pose the hydrocarbons existing in the depositin the form of kerogen and to distill shale oil from the shale in thechimney.

The shale oil is collected and flows to the surface through theproduction well.

, This technique offers distinct advantages over the methods Iheretofore considered. Nevertheless,"the 'efi'ectiv'eness of thistechnique is dependent on the success with which retorting of the oilshale in the relatively large chimney space can be accomplished. As aretorting gas is injected into the chimney through a gas inlet wellconnecting the chimney with the gaspumping equipment at the surface, ahot zone of sufficient temperature to support retorting is formed in thevicinity of the injection point. This hot zone can be advanced by theinjection of. additional retorting gas through the injection well.Initiating and supporting retorting of the shale in the chimney in thismanner is not entirely satisfactory, however, because of the difficultyencountered in initiating and advancing the hot zone throughout theentire chimney volume. In the absence of satisfactory retortingthroughout the chimney, the recovery of shale oil from the chimney willbe unduly restricted, and the economic feasibility of utilizing thistechnique will be diminished.

It is an object of the present invention, therefore, to provide animproved process for the in situ retorting of oil shale formations.

It is an object of the present invention to provide a process These andother objects are accomplished by the novel process of the presentinvention as hereinafter set forth.

SUMMARY OF THE INVENTION mits and facilitates the establishment of a hotzone substantially across the cross-sectional area of the chimney. Thisis accomplished by injecting the retorting fluid into the chimney spaceby means of at least one injection well positioned generallyhorizontally across the chimney. The retorting fluid is injected throughperforations in the injection well liner.

The injection of a retorting fluid into the chimney from a multiplicityof points permits the establishment of a hot. zone at a temperaturesufficient to support retorting across substantially the entire width ofthe chimney. By injecting retorting fluid through a series of injectionwells thus positioned, the establishment of the desired hot zonesubstantially across and around the entire cross-sectional area of thechimney may be accomplished.

The support and advancement of thehot zone throughout the chimney facecan readily be accomplished by continued injection of the initialretorting fluid or a suitable gas into the injection wells andconsequently into and around the crosssectional area of the chimney. Theinjection wells called for herein may be positioned either in the upperor the lower portion of the chimney, with the distilled shale oil beingrecovered through production wells in accordance with normal techniques.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fullydescribed hereinafter with reference to the attached drawings in which:

FIG. I is a side elevational view, partially in cross section, showingthe relative'positions of an injection well and a DETAILED DESCRIPTIONOF THE INVENTION In order to initiate and support retorting of the shaleacross and around the chimney formed by the detonation of a nucleardevicein a subsurface inan oilshale formation,'at least one injectionwell is positioned so that it extends generally horizontally across thewidth of the chimney. The injection well liner contains perforationsthrough which the retorting fluid may be injected into the chimney. Theretorting fluid is used to establish a hot zone in the chimney at atemperature capable of supporting retorting of the shale. Theprojectionof the retorting fluid through a series or multiplicity ofperforations in the generally horizontally extending injection wellliner facilitates the establishment'of a hot zone substantially acrossthe width of the chimney. Injection of the retorting fluid through agenerally vertically positioned injection well extending into thechimney would, on the other hand, result in the establishment of a morelocalized hot zone in the vicinity of the injection well outlet. Evenwith the use of very high injection volumes. the extending of the hotzone substantially across the width of thechimney would be difficult touccomplish. The present invention, therefore, permits the establishmentand support of a hot zone that enhances the retorting of the shale andthe recovery of the shaleoil from the chimney.

The injection well called for by the present invention can be providedby known drilling techniques. The injection well is drilled preferablyas a slant well by the so-called slant-hole drilling technique. Detailsof this drilling technique, which involves tilting the drilling rig, arenot included herein as this drilling technique is known and has beenemployed in conjunction with conventional petroleum-producing methods.

It is also possible to provide one or more injection wellbore holes thatextend downward from the earths surface in a generally verticaldirection with radially diverging bore hole extensions extending intothe chimney and across the chimney in a generally horizontal direction.The so-called directional drilling technique can be employed to providethe deviating bore hole extensions. Since directional drilling is also awell established technique that has been employed in conventionaloperations, further details of the manner in which the drilling isaccomplished are not included herein.

In order to provide means for injecting the retorting fluid generallyacross the width of the chimney, perforated liner extensions may beemployed in the portion of the injection well passing through thechimney. Altemately, plain liner extensions may-he employed andperforations may be-made after the liner leaving been placed. Techniquesfor perforating the concentrated after it has been positioned in theformation are well known in the, art. For example,'pressure may beemployed to blow out plugs in the liner or perforations may be made bychemical action.

1 injection of the retorting fluid into the chimney space may beaccomplished through one or more injection wells. Each well, of course,preferably will have a generally horizontally extending portion in thechimney. While one such injection well provides a series of injectionports across the width of the chimney, it may be desirable to employ twoor more of such injection wells in order to more fully cover thecross-sectional area of the chimney. From about two to about sixinjection wells would normally be sufficient for this purpose althoughadditional injection wells could also be employed. Coverage across andaround the cross-sectional area of the chimney can conveniently beachieved by positioning four injection wells at intervals at about 45around the circumference ofthe chimney. By extending each of these wellssubstantially across the width of the chimney, thus crossing at thecenter portion of the chimney, a multiplicity of injection ports can beprovided around the cross-sectional area of the chimney.

The various injection wells waste be positioned across the chimney atvarious elevations if desired. Generally, however, the injection well orwells will be positioned near the top of the chimney. The injectionwells can, however, be positioned near v the bottom of the chimney or atsome intermediate position in either the upper or lower portion of thechimney. it is also within the scope of'the present invention to injectthe retorting fluid sequentially through injection wells positioned atmore than one elevation in the chimney in order to facilitate therecovery of shale oil from the chimney space.

In FIG. 1 of the drawing, the chimney of fractured and crumbled shale ofhigh permeability is represented by the numetal 1. This chimney isformed by the detonation of a nuclear device generally positioned at thebottom of oil shale formation 2. Access well 3, which is drilled fromsurface 4 through overburden S and into oil shale formation 2 isemployed initially in order to place the nuclear device in position fordetonation. Tilted drilling rig 6 may be employed for the drilling ofproduction well 7 positioned at the base of chimney 1. This drilling rigmay also be employed in the drilling slant injection well 8 that ispositioned in the upper portion and near the top of chimney 2. As can bereadily seen from the drawing, injection well 8 is drilled so that tnthat extends across chimney 2 is positioned generally horizontally.Perforations generally represented by the numeral 9 are provided in theportion of injection well 8 extending across the chimney to providesuitable injection ports for the injection of retorting fluidsubstantially across the width of the chimney.

FlG. concentrated illustrates an embodiment of the present invention inwhich four injection wells are positioned in a radial pattern aroundchimney 2. The four wells are positioned at 45 intervals around thechimney, Each well extends across the width of the chimney and isprovided with perforations on substantially the entire portion crossingsaid chimney. This arrangement provides for a multiplicity of injectionports substantially around and across the cross-sectional area of theinsufficient to retort any appreciable portion of the available andrecoverable oil in the chimney. The retorting fluid, therefore, isinjected into the chimney in order to heat the chimney space to asufiicient temperature to support combustion. The retorting fluid may beany suitable material or combination of materials that will provide thenecessary heat to establish retorting conditions in the chimney. Theretorting fluid may conveniently comprise a combustion gas formed byburning a combustible-containing gas, such as methane or natural gas,with air or some other oxygen-containing gas. it is within the scope ofthe present invention to burn a combustible gas or liquid aboveground toform the combustion gas or to inject the combustible gas or liquidtogether with an oxygen-containing gas into the formation through theinjection well so as to form the combustion gas underground. It is alsowithin the scope of the invention to employ some other gas, such as aheated oxygen-free gas or steam as the retorting fluid.

The retorting fluid injected through the perforations in the generallyhorizontally extending injection well supports the hot zone formedacross the width of the chimney, by'conventionai ignition or burning atthe injection points, i.e. at the perforations, along the generallyhorizontally extending portion of the injection well in the chimney.While the temperature required in the hot zone in order to supportcombustion varies with the pressure in the chimney space, at temperatureof at least about 600 F. is ordinarily required at atmospheric pressure.Hot zone temperatures between about 700 F. and about 2500 F. mayconveniently be employed.

The amount of retorting fluid employed in the practice of the presentinvention is not critical and will vary depending on a number offactors, such as the retorting temperature employed, the extend of oilrecovered, the initial shale temperature and the like. Retorting gasquantities of from about 20 to about 5,000 standard cubic feet into therelatively cool shale formation per cubic foot of crumbled shale in thechimney have been proposed although the size of the chimney developedwill greatly influence the actual amount employed.

In another embodiment of the present invention, the hot zone may beestablished by the reaction of chemicals in the chimney, other than bycombustion, so as to generate the desired quantity of heat. For example,magnesium pellets may be injected into the chimney, together with wateror other suitable carrying medium, through the perforations in thegenerally horizontally extending injection wells. HCl may then beinjected into the chimney through the same perforations so as to contactand react with the pellets. Such a technique would not only furnish theresultant heat of reaction, but would have an additional advantage aswell. The reaction would result in the evolution of hydrogen that wouldtend to hydrogenate the kerogen in the chimney, thus tending to upgradethe shale oil recovered from the chimney. Numerous other reactants willreadily occur to those skilled in the art as suitable for injection intothe chimney to provide, by means of their heat of reaction, the heatnecessary to support tants employed, the injection of the reactantsthrough the perforations of the generally .horizontally extendinginjection wells of the present invention permits the establishment ofthe hot zone substantially across and around the cross-sectional area ofthe chimney.

After the hot zone has been established, it may be advanced in thedesired direction by continuous or intermittent injection of a gas thatadvances the heat front through the chimney. Air or anotheroxygen-containing gas can conveniently be employed for this purpose. Theoxygen content and rate of flow of the gas, together with the amount ofresidual combustibles in the formation, will determine the temperatureand the rate at which the heat wave is propogated through the chimney.

It has been suggested that a nuclear detonation may be used in therecovery of oil from Athabasca tar sands and similar formations as wellas from oil shale formations as disclosed herein. Recovery procedureswould follow essentially the same pattern as in the recovery of shaleoil. The present invention could also be employed in this procedure in asimilar manner as set forth herein.

In yet another embodiment, the horizontally extending injection wellsdisclosed herein may be employed in the retorting of oil shalesubstantially across an area of fractured and crumbled shale formed bythe detonation of conventional explosive device.

While the present invention has been described with reference toparticular embodiments thereof, it will be appreciated that variouschanges and modifications can be made therein without departing from thescope of the invention as set forth in the appended claims.

1. In the recovery of shale oil from a subsurface oil formation by meansof a nuclear explosion that creates a cavity in the formation that fillswith collapsing oil shale to form a chimney of fractured and crumbledshale of high permeability from which shale oil is recovered through aproduction well, an improved means of initiating and supporting in situretorting of the oil shale comprising injecting the retorting fluid intothe chimney through perforations in the liner of four injection wellspositioned at approximately 45 intervals along the periphery of thechimney area and extending generally horizontally in the chimney andrecovering the shale oil through at least one production well positionedin the chimney, whereby the retorting fluid is injected substantiallyacross the width of the chimney so as to facilitate in situ retortingthroughout the chimney.

2. The method of claim 1 in which said retorting fluid is injected intothe upper portion of the chimney and shale oil is recovered from thelower portion of the chimney.

3. The method of claim 1 in which the injection wells are positioned ina parallel configuration across the width of the chimney.

4. The method of claim 1 in which said generally horizontally extendinginjection wells cross one another so as to provide a multiplicity ofinjection points throughout the crosssectional area of the chimney.

5. The method of claim 1 in which the retorting fluid comprises the hotcombustion products obtained by burning a combustible fluid with anoxygen-containing gas.

6. The method of claim 5 in which said combustion products are formedabove ground and are injected into the chimney through said injectionwells.

7. The method of claim 5 in which said combustion products are formedbelow ground by burning the combustible fluid with an oxygen-containinggas after injection into said injection wells.

8. The method of claim 1 in which the retorting fluid comprises steam.

9. The method of claim 1 in which the retorting fluid comprises a gasheated to at least retorting temperature.

10. The method of claim 1 in which saidretorting fluid is injected intothe chimney until a hot zone is established therein of sufficienttemperature to support combustion and including the subsequent injectionof an oxygen-containing gas through said injection wells to advance thehot zone through the chimney.

11. The method of claim 1 in which the retorting fluid compriseschemical reactants injected into the chimney, said reactants being suchthat upon contact in the chimney a heat of reaction will be generated soas to furnish the heat necessary for retorting the fractured andcrumbled shale in the chimney.

12. The method of claim 1 in which the retorting fluid is injectedsequentially through said injections wells positioned at more than oneelevation in the chimney space.

2. The method of claim 1 in which said retorting fluid is injected intothe upper portion of the chimney and shale oil is recovered from thelower portion of the chimney.
 3. The method of claim 1 in which theinjection wells are positioned in a parallel configuration across thewidth of the chimney.
 4. The method of claim 1 in which said generallyhorizontally extending injection wells cross one another so as toprovide a multiplicity of injection points throughout thecross-sectional area of the chimney.
 5. The method of claim 1 in whichthe retorting fluid comprises the hot combustion products obtained byburning a combustible fluid with an oxygen-containing gas.
 6. The methodof claim 5 in which said combustion products are formed above ground andare injected into the chimney through said injection wells.
 7. Themethod of claim 5 in which said combustion products are formed belowground by burning the combustible fluid with an oxygen-containing gasafter injection into said injection wells.
 8. The method of claim 1 inwhich the retorting fluid comprises steam.
 9. The method of claim 1 inwhich the retorting fluid comprises a gas heated to at least retortingtemperature.
 10. The method of claim 1 in which said retorting fluid isinjected into the chimney until a hot zone is established therein ofsufficient temperature to support combustion and including thesubsequent injection of an oxygen-containing gas through said injectionwells to advance the hot zone through the chimney.
 11. The method ofclaim 1 in which the retorting fluid comprises chemical reactantsinjected into the chimney, said reactants being such that upon contactin the chimney a heat of reaction will be generated so as to furnish theheat necessary for retorting the fractured and crumbled shale in thechimney.
 12. The method of claim 1 in which the retorting fluid isinjected sequentially through said injections wells positioned at morethan one elevation in the chimney space.